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https://issues.apache.org/jira/browse/CALCITE-2688?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16693358#comment-16693358
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Zoltan Haindrich commented on CALCITE-2688:
-------------------------------------------
Note: there were some safeguards agains this in {{RelBuilder}}; but I think
that {{RexBuilder}} is also public api...and we might even reach type issues
during development.
The {{SqlOperator}} class has a method which is doing the return type
resolution - it's [api
doc|https://github.com/apache/calcite/blob/d32ee5c320938b5c34ce09df2276c9570c27a301/core/src/main/java/org/apache/calcite/sql/SqlOperator.java#L465]
doesn't state that it might return null; I propose to keep the api contract;
and throw an exception in case the resolution fails (and move the check from
RelBuilder there instead).
> Improve diagnosability when return type could not be inferred.
> --------------------------------------------------------------
>
> Key: CALCITE-2688
> URL: https://issues.apache.org/jira/browse/CALCITE-2688
> Project: Calcite
> Issue Type: Improvement
> Reporter: Zoltan Haindrich
> Assignee: Zoltan Haindrich
> Priority: Major
>
> Currently when the return type inferenence fails; a {{null}} is returned;
> while leads to an NPE very quickly - the resulting Exception is not
> informative at all.
> {code}
> @Test(expected = IllegalArgumentException.class)
> public void checkNoCommonReturnTypeException() {
> coalesce(vVarchar(1), vInt(2));
> }
> {code}
> example NPE:
> {code}
> java.lang.NullPointerException
> at java.util.Objects.requireNonNull(Objects.java:203)
> at org.apache.calcite.rex.RexCall.<init>(RexCall.java:59)
> at org.apache.calcite.rex.RexBuilder.makeCall(RexBuilder.java:242)
> at org.apache.calcite.rex.RexBuilder.makeCall(RexBuilder.java:254)
> at
> org.apache.calcite.test.RexProgramBuilderBase.coalesce(RexProgramBuilderBase.java:300)
> at
> org.apache.calcite.test.RexProgramTest.checkNoCommonReturnTypeException(RexProgramTest.java:753)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> {code}
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